1. Field of the Invention
This invention relates to a method of manufacturing an electron-emitting device and it also relates to an electron source and an image-forming apparatus such as a display apparatus incorporating an electron-emitting device manufactured by such a method.
2. Related Background Art
There have been known two types of electron-emitting device; the thermoelectron type and the cold cathode type. Of these, the cold cathode type include the field emission type (hereinafter referred to as the FE-type), the metal/insulation layer/metal type (hereinafter referred to as the MIM-type) and the surface conduction type.
Examples of the FE electron-emitting device are described in W. P. Dyke and W. W. Dolan, xe2x80x9cField emissionxe2x80x9d, Advance in Electron Physics, 8, 89 (1956) and C. A. Spindt, xe2x80x9cPHYSICAL Properties of thin-film field emission cathodes with molybdenum conesxe2x80x9d, J. Appl. Phys., 47, 5248 (1976).
MIM devices are disclosed in papers including C. A. Mead, xe2x80x9cThe tunnel-emission amplifierxe2x80x9d, J. Appl. Phys., 32, 646 (1961).
Surface conduction electron-emitting devices are proposed in papers including M. I. Elinson, Radio Eng. Electron Phys., 10 (1965).
A surface conduction electron-emitting device is realized by utilizing the phenomenon that the electrons are emitted out of a small thin film formed on a substrate when an electric current is forced to flow in parallel with the film surface. While Elinson proposes the use of SnO2 thin film for a device of this type, the use of Au thin film is proposed in G. Dittmer: xe2x80x9cThin Solid Filmsxe2x80x9d, 9, 317 (1972) whereas the use of In2O3/SnO2 and that of carbon thin film are discussed respectively in M. Hartwell and C. G. Fonstad: xe2x80x9cIEEE Trans. ED Conf.xe2x80x9d, 519 (1975) and in H. Araki et al.: xe2x80x9cVacuumxe2x80x9d, Vol. 26, No. 1, p.22 (1983).
FIG. 24 of the accompanying drawings schematically illustrates a typical surface conduction electron-emitting device proposed by M. Hartwell.
In FIG. 24, reference numeral 221 denotes a substrate. Reference numeral 224 denotes an electro-conductive film normally prepared as integrally with a pair of device electrodes 225, 226 by producing an H-shaped metal oxide thin film by means of sputtering, part of which eventually makes an electron-emitting region 223 when it is subjected to an electrically energizing process referred to as xe2x80x9celectric formingxe2x80x9d as described hereinafter. In FIG. 24, the horizontal area of the metal oxide thin film separating the pair of device electrodes 225, 226 has a length L of 0.5 to 1.0 mm and a width W of 0.1 mm. Note that the electron-emitting region 223 is only very schematically shown because there is no way to accurately know its location and contour.
As described above, the electroconductive film 224 of such a surface conduction electron-emitting device is normally subjected to an electrically energizing preliminary process, which is referred to as xe2x80x9celectric formingxe2x80x9d, to produce an electron emitting region 223.
In the electric forming process, a DC voltage or a slowly rising voltage that rises typically at a rate of 1V/min. is applied to given opposite ends of the electroconductive film 224 to partly destroy, deform or transform the thin film and produce an electron-emitting region 223 which is electrically highly resistive. Thus, the electron-emitting region 223 is part of the electronductive film 224 that typically contains fissures therein so that electrons may be emitted from those fissures. Note that, once subjected to an electric forming process, a surface conduction electron-emitting device comes to emit electrons from its electron emitting region 223 whenever an appropriate voltage is applied to the electroconductive film 224 to make an electric current run through the device.
Since a surface conduction electron-emitting device as described above is structurally simple and can be manufactured in a simple manner, a large number of such devices can advantageously be arranged on a large area without difficulty. As a matter of fact, a number of studies have been made to fully exploit this advantage of surface conduction electron-emitting devices. Applications of devices of the type under consideration include charged electron beam sources and electronic displays.
In typical examples of application involving a large number of surface conduction electron-emitting devices, the devices are arranged in parallel rows to show a ladder-like shape and each of the devices are respectively connected at given opposite ends with wirings (common wirings) that are arranged in columns to form an electron source (as disclosed in Japanese Patent Application Laid-open Nos. 64-31332, 1-283749 and 1-257552).
As for display apparatuses and other image-forming apparatuses comprising surface conduction electron-emitting devices such as electronic displays, although flat-panel type displays comprising a liquid crystal panel in place of a CRT have gained popularity in recent years, such displays are not without problems. One of the problems is that a light source needs to be additionally incorporated into the display in order to illuminate the liquid crystal panel because the display is not of the so-called emission type and, therefore, the development of emission type display apparatuses has been eagerly expected in the industry.
An emission type electronic display that is free from this problem can be realized by using an electron source prepared by arranging a large number of surface conduction electron-emitting devices in combination with fluorescent bodies that are made to shed visible light by electrons emitted from the electron source (See, for example, U.S. Pat. No. 5,066,883).
For a surface conduction electron-emitting device of the above described type, the electroconductive film is desirably made of a metal oxide having an electric resistance sufficiently greater than that of a metal film as in the case of the above described M. Hartwell""s electroconductive film 224 (FIG. 24). This is because a large electric current is required for the electric forming operation if the electroconductive film 224 has a low electric resistance when the electron-emitting region is produced by electric forming. The required electric current will be huge and beyond any practical level particularly when a large number of surface conduction electron-emitting devices need to be simultaneously subjected to an electric forming operation in the process of manufacturing an electron source comprising a plurality of surface conduction electron-emitting devices.
On the other hand, an electron source comprising a plurality of surface conduction electron-emitting devices and an image-forming apparatus incorporating such an electron source can be driven only by consuming electric power at an enhanced rate if the electroconductive film of each device has a high electric resistance.
In view of the above identified technological problems, it is therefore an object of the present invention to provide a method of manufacturing an electron-emitting device that can effectively reduce the drive voltage and the power consumption level of the device.
Another object of the invention is to provide an electron source and an image-forming apparatus that operate on a power saving basis.
Still another object of the invention is to provide an electron source comprising a plurality of electron-emitting devices that operate uniformly for electron emission and an image-forming apparatus incorporating such an electron source and capable of displaying high quality images.
A further object of the present invention is to provide a method of manufacturing an electron-emitting device that can effectively reduce the electric current for electric forming and the, power consumption level required for driving the device as well as an energy saving electron source comprising a plurality of such electron-emitting devices that operate uniformly for electron emission and an image-forming apparatus incorporating such an electron source and capable of displaying high quality images.
According to a first aspect of the invention, the above objects and other objects of the invention are achieved by providing a method of manufacturing an electron-emitting device comprising a pair of oppositely disposed electrodes and an electroconductive film inclusive of an electron-emitting region arranged between said electrodes characterized in that said method comprises a processing step of reducing the electric resistance of the electroconductive film arranged between the electrodes.
Preferably, said processing step of reducing the electric resistance of the electroconductive film arranged between the electrodes is a step of chemically reducing the electroconductive film.
According to a second aspect of the invention, there is provided an electron source comprising an electron-emitting device for emitting electrons as a function of input signals characterized in that said electron-emitting devices are produced by said manufacturing method.
According to a third aspect of the invention, there is provided an image-forming apparatus comprising an electron source and an image-forming member for forming images as a function of input signals characterized in that said electron source is an electron source comprising an electron-emitting device produced by said manufacturing method.